The present invention relates to oil-filled, pad-mounted electrical distribution transformers and in particular to a tank for such transformers.
A transformer tank is designed to house a transformer electrical core and coils. Conventional tanks are formed in the shape of a rectangular cube and comprise four vertical side walls, a horizontal top wall, and a horizontal bottom wall. During assembly, five of those walls are preassembled together by welding, leaving an opening to permit subsequent insertion of the core and coil assembly. Usually, the opening is provided at the top, although in some cases, it can be provided at one of the sides.
After that open structure has been leak tested, the transformer core and coil may be placed inside the tank through the open top. Then, utilizing holes formed in the front plate, the usual electrical connections are made, and the appropriate accessories are installed. The tank is then filled with oil to a prescribed level, and the top wall, e.g., a substantially flat or domed cover, is placed on flanges formed by bent upper ends of the side panels and is welded in place. The tank is then coated with a corrosion resistant film.
Since transformer tanks are often located in areas to which the general public has access, the presence of sharp corners on the tanks is avoided as much as possible. One way of avoiding the presence of sharp corners between the side panels is to form those panels of a single piece of sheet metal bent twice to form two rounded vertical corners (e.g. See Borgmeyer et al U.S. Pat. No. 4,533,786). Also, the floor plate and front plate could be integrally formed by bending a single metal sheet.
The width and height of the front plate are dictated by electrical and mechanical clearances between certain parts. For a given size transformer, the maximum horizontal depth of the tank interior is governed by necessary electrical and mechanical clearances for the core and coil. Therefore, the internal volume of the tank typically ends up being so large that it is necessary in some cases to add reinforcing members to prevent the vertical side panels and floor plate from being deformed by internal and external pressures.
Also, there is a risk of the floor plate becoming corroded due to contact thereof with water and other corrosive elements disposed on the surface of the pad support upon which the transformer is seated. If such corrosion is not detected at an early stage, there is a risk of the tank developing leaks through the floor plate.
Therefore it would be desirable to minimize or eliminate problems of the type discussed above, and to otherwise improve transformer tanks.